Your friend there may have to prepare the sponsor documents for
you. She has to show that she can accommodate you when you
are there. And she may has to show
1) I-139
2) bank account balance
3) letter from bank
4) her invitation letter to you
5) personal letter to consular
6) Proof of US citizenship
7) payrolls, tax returns,..
You should check them on immihelp.com. Good luck!

there is no restriction for your to travel on B2 mostly but
don't assume you will get 3months initially because its the
one who decides at the port of entry. Definitely there will
be questions waiting for you at port of entry and make your
answers prepared and your well answers will decide your
duration of stay and even there are chances to reject your
entry too.

it is healthy to reapply for b1/b2 visa quiet after 6months
after your visa rejected and there is no such limitations
that you can't reapply. b1/b2 is the easiest usa visa one
can obtain and in such your cases fails means then you have
to double check your supportive docs and more over you
should do your interview proper.
if you are applying for business visit then behave like a
business man in the interview and not just like a candidate!!